Many medical devices which utilize electric power have been developed for long term implantation. If the power required is low enough--such as with pacemakers, and various types of muscle and nerve stimulators, implanted batteries can reliably store enough energy for years of operation. These may utilize tiny amounts of power measured in milliamps using intermittent brief bursts of stimulation. Devices such as blood pumps, heart assist devices or total artificial hearts operate continuously and require thousands of times as much energy as pacemakers. A battery which powers a pacemaker for a decade would power an artificial heart for less than an hour.
Percutaneous leads are means of accessing the tissues beneath the skin. Many types of percutaneous leads have been developed and include catheters for fluid access, fabric-covered pneumatic tubes, and electric cables with large subcutaneous flanges for soft tissue ingrowth to fix the device in place and provide a barrier to bacterial infections. The effectiveness of most of these devices is limited.
A major cause of infection of percutaneous leads is trauma to the tissues where the device penetrates the skin. Motion of the tube or cable relative to the skin tears the cellular junction of the body tissue to the prosthetic material. This occurs repeatedly--prevents tight healing and permits bacteria to enter.
The most successful type of percutaneous lead developed to date uses rigid fixation to bone to prevent motion of the device and places the device in a position where virtually no motion of the skin over the bone occurs. This protects the junction of the skin and percutaneous lead from trauma. Skull-mounted devices of this type have proven highly effective (greater than 95% 10 year success) in hundreds of artificial hearing cochlear implant patients. The longest implant to date is 20 years and the patient continues to do well. In addition to excellent stabilization on the skull, the tissues of the scalp are highly vascular and adapted to resist wound infection, as an evolutionary mechanism to protect the brain.
For providing power to an artificial heart or assist device located in the chest, the skull-mounting position has the major disadvantage that wires must be tunneled through the tissues of the neck, and must withstand a great deal of flexing and torsional strain as the patient bends and turns the head and neck.
Tunneling to pass the cable through the neck tissues and across the chest wall to reach the heart involves trauma which should be minimized. A large-diameter flange is needed to achieve strong fixation of the percutaneous lead device to the skull, but is not compatible with minimizing trauma during tunneling. Excessive trauma can cause scarring, which may be cosmetically unfavorable, and can also result in infection. Additionally, in order to relieve strain on the cable, we have developed a method which utilizes a serpentine cable having several zig-zag loops as the cable lies along the neck. This requires several incisions which should be as small as possible.
For these and other reasons, the device of the present invention provides a power cable and connector part which is separable from the large diameter flange and is then attached to the flange after tunneling. This permits zig-zag tunneling with minimal trauma. A keyed configuration of the pedestal and connector is provided which permits the patient to safely plug and unplug the connector on the back or side of the head without seeing it.